Method for providing multiple sdp media flows in a single pop context

ABSTRACT

The invention relates to a method enabling multiple session description protocol media flows for one packet data protocol context. Therefore an indicator is sent from a P-CSCF to a user equipment indicating that a particular session description protocol media flow can be combined with further session description protocol media flows in a single packet data protocol context.

TECHNICAL FIELD

The invention relates to a method and means for setting up multiple SDP(Session Description Protocol) media flows for a PDP (Packet DataProtocol) context.

PRIOR ART

It has been recognised in 3GPP recently, that there needs to besimplification in the way SDP media flows are assigned to PDP contexts.The main driver for this is the charging requirements, whereby operatorswould like to bundle session and bearer level charges for particular SDPmedia flows.

The existing GPRS mechanisms as for example described in 3GPPspecification TS 23.060, Version 3.9.0 of October 2001, already allowQoS (Quality of Service) policing, and counting of packets on a PDPcontext granularity. The TFTs (Traffic Flow Template) in the GGSN(Gateway General packet radio service Support Node) allow furtherfiltering on the IP (Internet Protocol) level-user packet. There is thusa possibility to reuse these existing GPRS (General Packet RadioService) mechanisms to satisfy the charging requirements in a simplemanner. To this end, there has been some proposals to mandate one SDPmedia flow per PDP context. This in effect, allows the one-to-onecorrespondence of one PDP context to one SDP media stream, hence theGPRS QoS policing, and counting packets capabilities are reused.

However, there are drawbacks in implementing a one-to-one relationbetween SDP media flow and PGP context.

The current NSAPI (Network Service Access Point Identifier) code-pointlimit is 11. From a usage point of view, this could limit futureexpandability of IMS (IP Multi-media System), if the signalling PDPcontext, RTP/RTCP (Real Time Protocol/Real Time Control Protocol)separation, possibility for multiple chat sessions and other possiblefuture usages are taken into account. From a UTRAN (UniversalTerrestrial Radio Access Network), and SGSN (Serving General packetradio service Support Node) point of view, there are practical limits onthe maximum number of PDP contexts that can be active at the same time,otherwise, the solution becomes too expensive to the operator.

Thus it is object of the invention to provide a method and means thatovercome said drawbacks. This is achieved by the method of claim 1, theuser equipment of claim 4, the packet call state control function ofclaim 5 and the serving GPRS support node of claim 6.

SUMMARY

It is one object of the invention to provide a method for providingmultiple session description protocol media flows for one packet dataprotocol context. The method comprises the step of sending from apacket-call state control function to a user equipment, a sessioninitiated protocol message comprising an indication that a particularsession description protocol media flow can be combined with furthersession description protocol media flows in a single packet dataprotocol context. The step of receiving said message in the userequipment, the step of interpreting the indicator, the step of selectinga packet data protocol context, and of sending a set-up request messagefor setting up said packet data protocol context comprising anauthorisation token and identifiers of session description protocolmedia flows.

In an embodiment of the invention, the method the indication is sentfrom a home network of the user equipment to a visited network whereinthe user equipment is currently located and is cached in said visitednetwork before it is sent to the user equipment. In an embodiment of theinvention, the indication conveys information whether the home networkrequires policing for each media flow, counting of packets per mediaflow, or flow independent policing.

Another object of the invention is user equipment comprising electroniccircuitry adapted to interpret an indication received that a particularsession description protocol media flow can be combined with furthersession description protocol media flows in a single packet dataprotocol context, a selection unit for selecting further media flowsthat can be combined with the particular session description protocolmedia flow and a processing unit adapted to control the user equipmentand to initiate a sending of a set-up request message comprising anauthorisation token and identifiers of session description protocolmedia flows.

A further object of the invention is a packet-call state controlfunction adapted to send a message comprising an indication that aparticular session description protocol media flow can be combined withfurther session description protocol media flows in a single packet dataprotocol context.

Also object of the invention is a gateway general packet radio servicesupport node adapted to enforce a policy for handling a set-up requestfor a packet data protocol context wherein a single session descriptionprotocol media flow shall be combined with further session descriptionprotocol media flows, the policy received from a packet call statecontrol function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a part of a network as state of the art,

FIG. 2 depicts a signalling sequence for setting up a PDP context for aroaming subscriber, and

FIG. 3 depicts a resource reservation signalling flow.

DETAILED DESCRIPTION

Since the network and user equipment capabilities and limitation as wellas the charging models will vary it is not possible to find a singlemapping of IP flows/SDP media flows to PDP contexts that fulfils allrequirements. The invented method therefore provides the network thepossibility to inform the user equipment on how to map the media andcontrol flows described in SDP to PDP contexts. The mapping instructionsare be conveyed in SIP messages from the network to the user equipment.The mapping instructions will be carried for example in a (3GPPspecific) XML body in the SIP message. The mapping instructionsinformation allows the network to request several combination of flowson a PDP context, e.g. all flows on one PDP context, separate PDPcontexts for each RTP, RTCP, Signalling, etc.

For the specific case of mapping SDP media flows to PDP contexts, thefollowing is introduced, SIP messages are enhanced with an indicationfor user equipment when a particular media flow is possible to multiplexwith other media flows in a single PDP context. In a preferredembodiment of the invention, the default, or when the indication is notpresent, is one media flow per PDP context, i.e., the media flow cannotbe multiplexed with other media flows in a PDP context.

A user equipment according to the invention has the capability torecognise this indication. It is further adapted to process a callaccording to the indication and to request the set-up of an appropriatepacket data protocol context.

In the case that a subscriber is roaming, i.e. that her user equipmentis located in a visited network, the indication is sent from the homenetwork. The indication basically conveys the intention of the homeoperator either to have specific QoS policing/count of packets for aparticular media flow, i.e., the fine granularity case, hence the mediaflow should be alone in one PDP context, or to allow the simplifiedpolicing/no media flow level counting of packets nor media flow levelQoS policing, i.e., the course granularity case, hence multiplexing isOK. The decision which policy applies is at the home network since thehome network owns the services, and because it is home network decisionhow the bundling of session-bearer shall look like to their subscribers.

The visited network P-call state control function/PCF (Policy ControlFunction or Policy Decision Function) caches the indication sent fromthe home network, and enforces that the user equipment obeys the homenetwork request.

The user equipment sets up the PDP context of his choice, and includesthe necessary authorisation token and flow identifiers. It is possibleto multiplex different media flows in one PDP context if the homeoperator allows it, i.e., the indication is present.

The visited network enforces the indication with the following, if therequest for a particular media flow was that only one SDP media flow perPDP context is permitted, and the user equipment activates a PDP contextwith more than one flow identifiers the P-CSCF/PCF/GGSN then authorizesonly one media flow, downgrades the PDP context QoS to fit theauthorized QoS for the media flow, and notifies the user equipment ofthe media flow that was authorised via the PDP context response. Theuser equipment is then, in effect, notified to activate another PDPcontext for the other media flows. The GGSN enforces the uplink/downlikfilter, for example by means of TFTs. Said filter may be sent over theGo interface as depicted in FIG. 1. In another embodiment of theinvention, if there is an indication from the network for ‘nomultiplexing’ and the user equipment requires a single PDP contextassociated to more than one SDP media flow, the PDP context activationmay also simply be rejected, for example with an appropriate errorcause.

In the case that a subscriber roams into a visited network and ifmultiplexing is allowed for all media flows included in one PDP contextactivation, the P-CSCF/PCF/GGSN permits the PDP context activation, forexample after checking that the summed QoS is within the authorizedlimit of the sums. Therefore, however, no 3rd level will be implemented,no media flow level counting of packets nor media flow level QoSpolicing. At most only uplink/downlink filter like TFTs enforcements aredone per PDP context at the GGSN. Said TFTs may be sent down over the Gointerface between P-CSCF and Gateway GPRS support node. Theuplink/downlink filters may not provide functionality beyond what iscurrently possible with the TFT.

Regarding RTP/RTCP, as described above, the network notifies mappinginstructions information to user equipment, which enables the network torequest the combination on a PDP contexts, e.g. separate or common PDPcontext for RTP and RTCP.

To that end, for example a ‘RTCP’ indication flag is created and used bythe user equipment during PDP context activation. The user equipmentuses this flag to indicate to the network the intention of using the PDPcontext for RTCP packets. The network (GGSN/P-CSCF/PCF) authorises theuse of the ‘RTCP’ flag, according to the mapping instructionsinformation. For the case that a common PDP context is used, the P-callstate control function decision on the media flow applies to bothRTP/RTCP which are in effect, considered by the network as ‘one flow’.In SIP/SDP, RTCP is not explicitly described under the m=line, but isimplied to exist. RTP and RTCP have neighbouring port numbers, and areconsidered as being part of the same protocol.

For the case when a different PDP context is used for RTCP,authorisation from the P-CSCF/PCF may or may not be needed, depending onoperator choice. A suitable plain GPRS interactive bearer may also beused for all RTCP traffic, no ‘RTCP’ flag, which is charged on volumeand not bundled to the session, if the operator allows this.

In the following the invention will be described in more detail by meansof figures.

FIG. 1 depicts user equipment UE-A and a part of a network comprising aRadio access network RAN, a Serving GPRS support node SGSN, a GatewayGPRS support node GGSN, a packet call state control function P-CSCF, aserving call server control function S-CSCF, and a node performingcharging functions Cost CTRL Node. Depicted as a dotted line is the Gointerface between the packet call server control function P-CSCF and theGateway GPRS support node GGSN. In an embodiment of the invention theGateway GPRS support node GGSN receives over said Go interface anindication of the policy for setting up a PDP context. In a preferredembodiment of the invention it further receives over the Go interfacefilters for enforcing said policy.

FIG. 2 depicts signalling sequence for setting up a PDP context for aroaming subscriber between a user equipment UE2, a packet call servercontrol function P-CSCF2, a serving call server control function CSCF2,and a terminating network that is not depicted. In a first step 1 theuser equipment UE2 sends a SIP INVITE request, containing an initialSDP, to the packet call server control function P-CSCF2, determined viaa CSCF discovery mechanism. The initial SDP may represent one or moremedia for a multi-media session. The packet call server control functionP-CSCF2 of the visited network forwards the message to the serving callserver control function S-CSCF2 of the home network of the userequipment UE2 in a next step 2 a. The packet call server controlfunction P-CSCF2 knows for example from the registration procedure theserving call server control function S-CSCF2 of the user equipment UE2.

In an embodiment of the invention wherein the home network of the userequipment performs configuration hiding, the messages sent between thepacket call server control function and the serving call server controlfunction are sent via an intermediate call server control function thatis performing the configuration hiding function for the home networkoperator.

The serving call server control function performs service control whichwill be described in more detail by means of FIG. 3. If the result ofthe service control is that the context shall be set-up, the servingcall server control function forwards the message to the terminatingnetwork. In a next step 5, the serving call server control functionS-CSCF receives the media stream capabilities of the destination in anoffer response message. The serving call server control function S-CSCFadds the indication that a particular session description protocol mediaflow can be combined with further session description protocol mediaflows in a single packet data protocol context to the offer responsemessage and sends it to the packet call server control function P-CSCF2in a next step 6 a. The packet call server control function P-CSCF2caches the indicator in a next step 7 and authorizes quality of serviceresources. In a next step 8 it sends an offer response to the userequipment UE2. The user equipment UE2 receives said message, interpretsthe indicator, selects a packet data protocol context, and sends aset-up request message for setting up said packet data protocol contextcomprising an authorisation token and identifiers of session descriptionprotocol media flows.

FIG. 3 depicts a resource reservation signalling flow between a userequipment UE3 a serving GPRS support node SGSN3, a Gateway GPRS supportnode GGSN3 and the packet call server control function P-CSCF3. The userequipment UE3 sends an Activate (Secondary) PDP Context message to theserving GPRS support node SGSN3 with UMTS QoS parameters. The userequipment UE3 includes Binding Information in the Activate PDP Contextmessage. In a next step 2 the serving GPRS support node SGSN3 sends thecorresponding Create PDP Context message to the Gateway GPRS supportnode GGSN3. In a following step 3 the Gateway GPRS support node GGSN3sends a COPS REQ message with the Binding Information to a PDF (PolicyDecision Function) in order to obtain relevant policy information. ThePDF sends a COPS DEC message back to the Gateway GPRS support node GGSN3in a next step 4. Afterwards the Gateway GPRS support node GGSN3 sends aCOPS RPT message back to the PDF. The Gateway GPRS support node GGSN3maps IP flow based policy information into PDP context based policyinformation and uses the PDP context based policy information to acceptthe PDP activation request, and sends a Create PDP Context Responsemessage back to the serving GPRS support node SGSN3 in a following step6. RAB setup is done by the RAB Assignment procedure in a next step 7.The serving GPRS support node SGSN3 sends an Activate (Secondary) PDPContext Accept message to the user equipment UE3.

1-6. (canceled)
 7. A method for providing multiple session descriptionprotocol media flows for one packet data protocol context, comprisingthe steps of: sending, from a packet-cscf to a user equipment, a sessioninitiated protocol message comprising an indication that a particularsession description protocol media flow can be combined with furthersession description protocol media flows in a single packet dataprotocol context; and receiving said message in the user equipment,which performs the steps of: interpreting the indicator; selecting apacket data protocol context; and sending a set-up request message forsetting up said packet data protocol context, said message comprising anauthorization token and identifiers of session description protocolmedia flows.
 8. The method according to claim 7, wherein the indicationis sent from a home network of the user equipment to a visited networkwherein the user equipment is currently located and is cached in saidvisited network before it is sent to the user equipment.
 9. The methodaccording to claim 8, wherein the indication conveys informationindicating whether the home network requires policing for each mediaflow, counting of packets per media flow, or flow independent policing.10. User equipment for providing multiple session description protocolmedia flows for one packet data protocol context, said equipmentcomprising: electronic circuitry adapted to interpret an indicationreceived by said equipment that a particular session descriptionprotocol media flow can be combined with further session descriptionprotocol media flows in a single packet data protocol context aselection unit for selecting further media flows that can be combinedwith the particular session description protocol media flow; and aprocessing unit adapted to control the user equipment and to initiatethe sending of a set-up request message comprising an authorisationtoken and identifiers of session description protocol media flows.